1. Field of the Invention
The present invention relates to a sheet feeding apparatus for feeding one sheet each by separating from a stacked state of sheets, regardless of the sheet size, when sheets of single-form documents or recording paper are used in plural sizes in a copying machine or the like.
2. Description of the Prior Art
In a copying machine equipped with a recirculating document handler (RDH) for stacking up documents of single form in a plurality, separating and feeding the documents one by one from the top side or bottom side, and returning to the stacked position after reading the documents in the bottom side or top side, a sheet feeder is used, such as the feeding apparatus of documents and the feeding apparatus of separating and feeding the stacked recording sheets one by one. In printing apparatus and photographic printing device, too, an apparatus for separating and feeding stacked recording papers is employed. In such paper feeding device, it is necessary to separate the stacked sheets one by one, and various separating methods are known, such as the air flow separating method, separating claw method, and method for separating sheets by using a roller rotating in a reverse direction of sheet feeding direction.
As an example of the prior art of separating sheets by using air flow, the structure of a paper feeder is shown in FIG. 1, a side view, and in FIG. 2, a plan view. This composition is, for example in a copying machine of RDH method, a paper feeder 1 for feeding by separating the stacked recording papers one by one. The paper feeder 1 is provided with a support tray 3 on which recording papers 2 are stacked up.
At the downstream side of the feeding direction A1 of the recording paper 2 and near the middle of the widthwise direction of the support tray 3 intersecting with the feeding direction A1, a notch 4 is formed, and a feed belt 7 stretched on a pair of rotating rollers 5, 6 disposed beneath the support tray 3 and having many penetration holes formed is exposed at this notch 4. Between the rotating rollers 5, 6 is arranged an air intake duct 8 opposite to the notch 4 across the feed belt 7, and the recording paper 2 on the support tray 3 is attracted by vacuum to the feed belt 7, and is fed in the feeding direction A1 by running and driving of the feed belt 7.
On the other hand, since there is a possibility that plural recording papers 2 on the support tray 3 be attracted and fed together by the feed belt 7, an air injection duct 9 is disposed above the downstream side of the feeding direction A1 from the support tray 3, and nozzles 10b to 10e parallel to the feeding direction A1 are communicated with one another.
At this stage, in order to improve capability of separating relatively large-sized recording papers 2, the array width L11 of the nozzles 10b to 10e disposed in the direction perpendicular to the feeding direction may be extended. In such a case, when the recording paper 2 having a width of smaller than the array width L11 is fed, the air flows from the nozzles 10b, 10e are passed without meeting the upstream ends of the recording papers 2, thereby flapping the lateral ends 2a, 2b of the recording paper 2. In this case, the stacking state of the recording papers 2 stacked within the paper feeder 1 is disordered which may in turn result in duplicate feed or feeding failure of the recording papers 2. Also in the case where the recorded papers 2 to be used are relatively small-sized, the sheet separating capability by the air flows from the nozzles 10b to 10e becomes excessive and thereby the small-sized recording papers are liable to be dispersed within the paper feeder 1.
In order to prevent such occurrences, the array width L11 may be reduced. In such a case, the area of a separation region 17, which is created by the air from the air injection duct 9 entering between the recording papers 2 and separating the recording papers 2 one from another, becomes relatively smaller compared with a non-separation region 18 in which the recording papers 2 are mutually stuck together. Accordingly, when the bottommost recording paper 2 is fed with being vacuum attracted to the feed belt 7, there are cases in which the duplicate feed may occur due to the friction in the non-separation region 18.
"Sheet feeding apparatus" disclosed in Japanese Laid-open Patent No. 58-78932 is given as another example of the prior art. U.S. Pat. No. 3,198,514 and Japanese Patent Publication No. 55-19859 respectively disclose similar configurations to the one of the invention. Such configuration is shown in a top plan view of FIG. 3. This configuration is similar to the one of the foregoing prior art and like reference numerals designate like or corresponding parts.
In this prior art, in addition to the nozzles 10b to 10e arranged in parallel to the feeding direction A1 in the foregoing embodiment, a plurality of nozzles 10a, 10f directed substantially at the widthwise center of the recording paper 2 are arranged outside the nozzles 10b to 10e in the array direction thereof with all the nozzles communicating with one another. Even the prior art thus constructed has similar drawbacks as the foregoing prior art.
Accordingly, in the case where the recording papers are limited to predetermined types, each of the foregoing prior arts demonstrates relatively satisfactory sheet separating capacity. However, in terms of versatility of effectively separating the recording paper sheets of a wide variety of sizes or quantities, the prior arts do not demonstrate sufficient versatility since they are liable to meet a sheet separation failure or feeding failure. Accordingly, a sheet feeding apparatus is desired which has capability of effectively separating the recording paper sheets of a wide range of sizes and quantities.